Physiology 1- body fluid compartments Flashcards
What is osmolarity?
concentration of osmotically active particles present in a solution
What are the units for osmolarity?
osmol/l (mosmol/l)
What 2 factors need to be known in order to calculate osmolarity?
the molar concentration of the solution; number of osmotically active particles present
What is the difference between osmolality and osmolarity?
osmolality has units of osmol/kg whereas osmolarity has
What is the osmolarity of body fluids?
around 300mosmol/l
What is tonicity?
the effect a solution has on cell volume
What are the 3 types of tonicity of a solution?
hypo-; hyper-; iso-
What does tonicity take into accoutn in addition to osmolarity?
the ability of a solute to cross the cell membrane
What 2 compartments does total body water exist as?
ICF and ECF
What makes up ECF?
plasma; interstitial fluid; llymph and transcellular flui
Give examples of transcellular fluid?
pleural fluid and CSF
How can the vlume of body fluid compartments be measured?
tracers
What is the equation for distribution volume when using a tracer?
distribution volume = Qx (known quantity of tracer)/ concentration of X in compartment
What is insensible fluid loss?
loss of water that the body has no physiological control over
How are the kidneys involved in water balance?
water balance is maintained by increased water ingestion; decreased excretion of water by the kdineys alone is insufficient to maintain water balance
Why can decreased excretion of water by the kidneys not maintain water balance?
some water always has to be excreted by the kdineys as some metabolic waste products can only be excreted in solution
What is the concentration of sodium in the ECF like in comparison to ICF?
higher in ECF (we evolved from fish, our internalised environment (ECF) is like the sea-salty!)
What are the main ions in the ECF?
Na; Cl and bicarb
What are the main ions in the ICF?
K; Mg and negativley charged proteins
Why is the regulation of fluid and electrolyte balance tightly intertwined?
changes in solute concentration lead to immediate changes in water distribution
What is fluid shift?
movement of water between the ICF and ECF in response to an osmotic gradient
What happens if the osmotic concentration of the ECF increases>
water shifts into ECF from ICF to restore osmotic equilibrium
What are the 3 challenges to fluid homeostasis?
gain or loss of water; gain or loss of NaCl; gain or loss of isotonic fluid
What happens if there is a gain or loss of water?
there is a similar change in ICF and ECF volumes; both increase or decrease (osmotic equilibrium is maintained)
What happens if there is gain or loss of NaCl?
PM is relatively impermeable to NaCl so water compensates to maintain osmotic equilibrium
What happens if there is a gain or loss of isotonic fluid?
there is no change in fluid osmolarity, there is a change in ECF volume only
How do the kidneys fit into fluid homeostasis?
kidney alters composition and volume of ECF
Why is maintaining electrlyte balance important?
total electrolye concentrations can directly affect water balance; the concentrations of indiviual electrolytes can affect cell function
What makes up more than 90% of the osmotic concentration of the ECF?
sodium salts
What happens if there is a decrease in potassium plasma concentration?
muscle weakness–paralysis; cardiac irregularities–cardiac arrest
Why is regulation of ECF volume important?
long-term regulation of BP
